Backrest for a chair



FIG. 1 is a perspective view of backrest for a chair showing my new design;

FIG. 2 is a front side elevational view thereof;

FIG. 3 is a rear side elevational view thereof;

FIG. 4 is a left side elevational view thereof, with the right side elevational view being a mirror image thereof; and,

FIG. 5 is a top plan view thereof; and with no ornamentation being claimed for the bottom plan thereof. 

CLAIM The ornamental design for backrest for a chair, as shown and described. 